Machine for thread rolling



Aug. 7, 1962 D, H PRUTTON 3,048,065

MACHINE FOR THREAD ROLLING Original Filed Oct. 21, 1953 3 Sheets-Sheet 1 El g4 Aug. 7, 1962 D. H. PRUTTON 3,048,065

. MACHINE FOR THREAD ROLLING Original Filed Oct. 21, 1953 3 Sheets-SheetZ '#12 E; I Q i IN V EN TOR. nN/f'z. l Par/fray Aug. 7, 1962 D. H. PRUTTON l 3,048,065

MACHINE FOR THREAD ROLLING Original Filed Oct. 21, 1953 'o' Sheets-Sheet 3 INVENTOR. .D4/Wfl. H. Pm/rra/v @rra/entr.;

United States Patent Otice v 3,@4h5- patented Aug. 7, 1962 6 Claims. (Cl. Sti-7) This invention relates to improvements in a thread rolling machine and more particularly to a machine for rolling threads on blanks or work pieces having generally cylindrical surfaces.

This application is a division of my copending United States application led October 2l, 19593, entitled Machine for Thread Rolling, Serial No. 387,378, now abandoned.

One of the objects of the present invention is to provide a novel and improved thread rolling structure for rolling threads on generally cylindrical surfaces and more particularly on hollow blanks or Work pieces having such surfaces.

A further object of the invention is to provide substantial improvements in the thread-forming operation by means of the novel and improved positional relationship of the thread forming die and associated parts and/ or the length of the thread rolling die contact with the workpiece.

Other features of this invention reside in the arrangement and design of the parts for carrying out their appropriate functions.

Other objects and advantages of this invention will be apparent from the accompanying drawings and description and the essential features will be set forth in the appended claims.

In the drawings,

FIG. 1 is a top plan View of the first form of the present invention;

FIG. 2 is a vertical sectional view taken along the line 2--2 through the thread rolling machine in FIG. l;

FIG. 3 is an enlarged vertical sectional -view taken along the line 3 3 of FIG. 1 showing the blank or workpiece of the hollow head set screw type, such as an Allen head, with a generally cylindrical peripheral surface having a thread beginning to tbe rolled or formed thereon;

FIG. 4 is a vertical sectional view taken along the line 4-4 of FIG. l, showing the biank or work piece of FIG. 3 having a substantially finished thread rolled thereon;

FIG. 5 is a vertical sectional view, corresponding to FIG. 4, but showing a bolt with a longitudinal central hole drilled therethrough;

FIG. 6 is a partial top plan View, corresponding to FIG. 1, of a second form of the present invention.

FIG. 7 is a vertical sectional view taken along the line 7-7 of FIG. 6; while FIG. 8 is a partial top plan view, corresponding to FIG. 6 of a third form of the present invention.

Speaking iirst generally, the novel apparatus now to be described herein comprises means for forming or rolling external and/or internal threads on generally cylindrical blanks or workpieces between generally cylindrical surfaces with at least one having a roll thread die form thereon. The diiferent forms of the thread rolling machine disclosed in the present application are especially designed for rolling threads on hollow blanks or work pieces with the thread rolling pressure applied gradually as the generally cylindrical work piece or blank progresses so that there is no possibility of crushing or collapsing the hole. This latter type of thread rolling requires a long die length for engagement so that the thread rolling pressure will be applied gradually.

Although each form of the invention disclosed hereinafter moves along a circular path during the thread rolling operation so that the thread rolling machine will be compact, it should be clearly understood that this invention includes other types of thread rolling machines wherein the work piece moves along a straight line or any other desired path. Also, although the machines disclosed hereinafter are specifically designed for applying thread rolling pressure gradually to hollow work pieces, it should be readily understood that solid work pieces could be roll threaded therein equally Well.

Each form of the invention has a similar frame and drive means so only the structure shown in FIG. 2 will be described in detail. A base 10 in FIG. 2 supports and is secured to a table 11 by connecting cabinet side walls 12. Extending upwardly through the center of the table 11 is a spindle `14 for causing the relative movement between the parts in the thread rolling operation. Although the table and spindle in each form of the invention are of slightly different structure, their mode of operation and structural support is always-basically the same. The spindle 14 is geared through conventional speed reduction gearing in a housing 18 to a pulley 19. A motor 2G drives pulley 19 by means of a V-belt 21. The motor is carried on a bracket 22 which is hinged to the housing 18 with the housing in turn being attached to table i-i. The tension on the belt l21 is maintained yby part of the Weight of the hinged motor assembly. The balance of the motor weight is supported by the adjustable suspension bolt 23.

Pulley 19 is attached to one end of a shaft 2S which at a spaced point therefrom is provided with suitable gear means (not shown) linking it with the aforesaid speed reduction gearing. Either the pulley 19 or a hand wheel secured to the shaft 2.5 may ybe manually turned to position spindle 14 to any suitable position for assembly or adjustment purposes of the machine.

The first form of the invention, shown in FlGS. 1 to 5 inclusive, is used for rolling external threads on work pieces with each having a generally cylindrical peripheral surface. The thread rolling machine is constructed so that the thread rolling pressure is applied gradually `by a plurality of contiguous die shoes arranged in tandem and individually adjustable.

A first thread rolling member located at the center of table 11 includes spindle 14 carrying a tapered hub 30 in FIG. 2 with an annular flange 31 secured immediately therebelow upon which a die ring 36, ei-ther of solid annular form or made up of segments but with a continuously threaded surface, is secured by bolts 37 threaded into the lflange 31. Die ring 36, rotatable about a central vertical axis, has a thread rolling die form on its generally cylindrical peripheral surface on which the generally cylindrical periphery of each work piece rolls during thread forming.

A second thread forming member secured to the top of table 11 comprises a plurality of outer die shoes or seg-` ments 46 of anyvsatisfactory number but shown as six in number in FIG. 1. These outer die segments 46 are adjustably attached to the top of the table 11 in contiguous relationship to form -a continuous threaded inner vertical concave face, machined to be complementary to the peripheral convex face of the annular die ring 36. Not only the die ring 36 but also the outer dies 46 have formed thereon in opposing relationship helical crests and grooves equal in pitch and other significant dimensions with the thread to be formed on a blank or Work piece when they cooperate together.

Since each outer die shoe 46 is similarly fixed with respect to table 11, the description of one will suffice. The same reference characteristics are used for each outer die shoe and its securing structure. Die shoe 46 interfits by a generally dovetail construction at 47 with a die holding block 4S and at 47a with `a clamp iinger 49 supplied by means of bolts 50i, as best seen in FIG. l. Vertical displacement of die 46 is prevented by a clamping bridge 51 retained on block 4S by bolt 52. The bridge is slidable endwise if desired as permitted by la slot 51a through which the shank of bolt 52 passes. The bolts, of course, msut be slacked off to permit such endwise movement of the bridge. Thus, die 46 may be removed and another replaced without removal of rblock 48. This die holding block 4S is retained on table 11 by bolts 56, the shanks of the bolts having limited clearance from the walls of the apertures in block 48 through which they pass to permit minor adjustment of block and die positions before finally tightening bolts 66. A back-stop block `57 is attached to table 11 by bolts 58, and it is horizontally pierced by threaded abutment bolts 59 which are advanced from several angles lto serve both in withstanding the stresses from the threading operation and in effecting positional adjustment of the die holding block 48 before bolts 56 are tightened down.

It should now be apparent that the work piece or blank, either hollow set screw 70 in FIGS. l, 3 or 4 or the hollow bolt 71 in FIG. 5, can be rolled in a clockwise direction in FIG. l from the FIG. 3 roughing position to the FIG. 4 finishing position when the annular die 36 is rotated by the spindle 14. A work piece 70, having a generally cylindrical peripheral surface to be threaded, is rolled between the generally cylindrical, continuous die surface formed by the contiguous outer die `shoes 46 and the generally cylindrical peripheral die surface on the die ring 36. These generally cylindrical die surfaces are approximately the same distance apart at all points but are positioned by their supports slightly closer together in the work piece advancing or clockwise `direction so that `the threads will be finished as the work piece travels clockwise. The thread rolling pressure is applied gradually to prevent collapsing of the hole in the hollow set screw.

The `second and third form of the invention in FIGS. 6, 7 and 8 have the thread rolling taking place in a circular path with the thread rolling pressure being applied gradually, to prevent collapse of the hollow work piece, by a progressive cam track effective against a cooperating roller follower. Comparable parts in the three different forms of the invention are shown by corresponding reference numbers but with the 100 prefix applied to the second form in FIGS. 6 and 7 and the 200 prefix applied to the third form in FIG. 8.

The second form of the invention in FIGS. 6 and 7 is designed for rolling external threads on work pieces with generally cylindrical peripheral surfaces of the type roll threaded in the first form of the invention in FIGS. 1 to 5 inclusive. The rst or center die member 136 in FIGS. 6 and 7 is stationary as contrasted with the rotating die ring 36 in FIG. l. A sleeve 135 is fixed to the housing 18 and has a flat disk 136 secured to its upper surface. This flat disk 136 with a generally cylindrical peripheral surface has a threaded rolling die form thereon on which the generally cylindrical peripheral surface of each work piece will roll during the threading operation.

A second member is mounted for rotation about the thread rolling disk 136 and on the vertical central axis of the machine. It comprises -an annular spindle 114 in FIG. 7 extending upwardly from within the housing 18 and through the `table 111 with this -spindle 114 being driven by the motor 2t? to rotate concentric with the peripheral generally cylindrical surface of die member 136. A plurality of radially movable, circumferentially spaced slides 148 in FIGS. 6 and 7 are mounted on the top of the annular spindle 114 for generally radial reciprocation toward and away from the thread rolling peripheral generally cylindrical surface of die 136. Each radial slide 148 has spaced generally cylindrical thread rolling dies 146, 146 with each having a peripheral generally cylindrical surface with a thread rolling die form thereon. Each die 146 is freely rotatable on a vertical pin 147 secured to the slide 148. Each roll die 146 is located outwardly from but always approximately the same distance from the generally cylin.

drical peripheral thread rolling surface on die 136, as seen in FIG. 6, so that a work piece or blank 170 can be held between each pair of roll dies 146 and the surface of die 136 for rolling a thread on its generally cylindrical peripheral surface.

As mentioned before in describing the FIG. l machine, the work piece in the present form of the invention Ialso moves in a clockwise direction from the left toward the right in FIG. 6 when traveling through the machine for rolling the thread from thereon. Means is provided for pushing the generally cylindrical die thread rolling surfaces on dies 146 and 136 Vcloser together as the work piece moves clockwise in the advancing direction. This takes the form in the present disclosure of a cam made up of a plurality of cam segments 162 in FIGS. 6 and 7 secured to tlie top of the table 111 by bolts 163 so as to be fixed relative to the first or stationary die member 136 and to remain stationary. A coacting follower roller is mounted for free rotation on a vertical pin 161 secured to each slide 148. The Cam segments 162 are arranged to urge the spaced die rolls 146, 146 on each slide 148, as it moves clockwise in the advancing direction, toward the thread die form on the periphery of die 136 for gradually rolling the thread form deeper on the generally cylindrical surface of the work piece 171) as it advances in the clockwise direction.

Although the center die 136 has been described as stationary or fixed with respect to the housing 18 and table 111, adjustment can be provided for wear. The die 136 will generally remain stationary during operation, but the die may be rotated counterclockwise after wear has occurred so as to move the worn finishing die surface counterclockwise closer to the roughing end of the machine so that the unused die surface immediately clockwise from the finishing end will be brought into finishing position.

It should be noted that since the radial slide 148 is traveling in the clockwise direction between the roughing and the finishing operations and the cam segments 162 are always pushing the cam followers 16) closer toward the center `against the resistance of work piece to the thread rolling operation, no spring is required to keep the cam follower roller 161) up against the cam surface. The resistance to deformation of the work piece, as this resistance is gradually overcome, performs this function.

The third form of the invention in FIG. 8 is designed for rolling internal threads on work pieces having concentric internal and external generally cylindrical surfaces. The first or center member 236 in FIG. 8 is stationary, similar to die member 136 in FIG. 6, as contrasted with the rotating die ring 36 in FIG. l. A sleeve 235 is fixed to the housing 18 and has -a flat disk 236 secured to its upper surface. This flat disk 236 has a gener-ally cylindrical peripheral surface on which the generally cylindrical peripheral surface of each work piece will roll during the threading operation.

A second member is mounted for rotation about the disk 236 and on the vertical central axis of the machine. It comprises an annular spindle 214 in FIG. 8 extending upwardly from within the housing 18 and through the table with this spindle 214 being driven by the motor 20 to rotate concentric with the peripheral generally cylindrical surface of member 236. A plurality of radially movable, circumferentially spaced slides 24S, only one being shown in FIG. 8, are mounted on the top of the annular spindle 214 for generally radial reciprocation toward and away from the peripheral generally cylindrical surface of member 236. Each radial slide 248 has a generally cylindrical thread rolling die 246 with a peripheral generally cylindrical surface having `a thread rolling die form thereon. Each die 246 is freely rotatable on a vertical pin 247 secured to its slide 248. The roll die 246 is located outwardly from but always about the same distance from the generally cylindrical peripheral rolling contact surface on member 236, as seen in FIG. 8, so that a work piece or blank 270 can be held between the roll die 246 and the peripheral surface of membe'r 236 for rolling a thread on its generally cylindrical bore or internal surface.

As mentioned before in describing the FIG. 1 machine, the work piece in the present form of the invention also moves in a clockwise direction from the left toward the right in FIG. 8 when traveling through thevmachine for rolling the thread form thereon.Y Means is provided for pushing the generally cylindrical die thread rolling surface on dies 246 and the generally cylindrical peripheral surface on member 236 closer together as the work piece moves clockwise in the advancing direction. This takes the form in the present disclosure of ya cam made up of a plurality of cam segments 262 in FIG. 8 secured to the top of the table so as to be fixed relative to the first member 236 and to' remain stationary. A coacting follower roller 260 is mounted for free rotation on a vertical pin 261 secured to each slide 248. The cam segments 262 are arranged to urge the die roller 246 on each slide 248, as it moves clockwise in the advancing direction, toward the periphery of member 136 for gradually rolling the thread form deeper on the generally cylindrical bore surface of the work piece 270 as it advances in a clockwise direction.

Of course, both the external and internal generally cylindrical surfaces of workpiece 270 can have thread forms rolled thereon simultaneously if desired, by having a thread rolling die surface, corresponding to that on die 136 in FIG. 7, on the peripheral generally cylindrical surface of disk 236 in FIG. 8.

Both the second form (FIGS. 6 and 7) and the third form (FIG. 8) of the invention can be properly designed for loading and unloading the work pieces 170 and 270 thereon. One suitable construction would be to form a notch in the generally cylindrical peripheral surface of die 136 -and disk 236 between the free ends of the cam segments (located in the arc extending clockwise between the finishing end and the roughing end) so that each work piece can be inserted between or withdrawn from between or withdrawn from between the thread rolling members. Another type of loading and unloading structure would withdraw the radial slides 148 and 248 away from the periphery of the die 136 or disk 236 respectively for loading and unloading.

Although center member 136 and 236 in FIGS. 6 and 8 respectively have been described as stationary, while spindles 114 and 214 rotate about the central vertical axis, each 4center member can also rotate about said axis by being geared to its spindle by gearing in housing 1S. A choice of gearing between each member and spindle will make it possible to vary within a wide range the relative rotational speed therebetween so that for a given arcuate cam length 162 or 262, the number of work piece rotations may be greater than (if spindle and center member rotate in opposite directions) or less (if both rotate in same direction) than when the center member is stationary. Hence, a thread may be rolled onto a hollow work piece by a greater number of revolution when rotation is in opposite directions than if the center member were stationary so as to give a more gradual thread formation with less pressure exerted on the work piece.

It should now be apparent that all forms of the invention operate generically the same. Each form of the invention provides a machine for rolling threads on workpieces with generally cylindrical peripheral surfaces. The machines in FIGS. l and 6 roll external threads on the generally cylindrical peripheral surfaces while the machine in FIG. 8 rolls internal threads on work pieces having concentric internal and external generally cylindrical peripheral surfaces. Each machine comprises a first or center member (36, 136, or 236) having a generally cylindrical peripheral surface with a thread rolling die form thereon on members 36 and 136. In each machine, the

ygenerally cylindrical outer surface of each work piece rolls on this generally cylindrical peripheral surface of the first member during theA thread rolling operation. Each machine has a second member (die shoes 46, spindle 114 or spindle 214 and appurtenant parts) with a generally cylindrical die surface (on dies 46 or on roll dies 146 or 246) located outwardly from but always approximately the same distance from the generally cylindrical peripheral surface on the first member. Both the first and second member in each form of the invention are connected together so that at least one or both of the members are rotated about the central axis of the first member so as to move relative to each other with the work pieces rolling between the generally cylindrical peripheral surfaces and having a thread rolled thereon. Each machine is provided with means `for pushing or positioning the thread rolling die surfaces on the second member closer to the `generally cylindrical peripheral surface on the first member as the work piece advances in the clockwise direction from the roughing to the finishing position. This takes the form in FIG. l of an inward placement of the outer die shoes 46 with each outer die shoe 46 being located closer to the `central vertical machine axis than the immediately preceding counterclockwise die shoe. In FIGS. 6, 7 and 8 this means takes the form of the cam, roller follower and the `radial slide construction.

As mentioned before, each machine causes the thread rolling pressure to be applied gradually as the work piece cylinder progresses through the machine so that the hollow work piece will not collapse. This requires a long die length or engagement with the work piece. Satisfactory results have been obtained when each work piece has a rolling contact with the thread rolling die form surface for at least and in some cases, approximately 270 of the peripheral surface of the rst member (36, 136 or 236). For example, FIG. l shows that dies 36 and 46 each have a thread `form extending `continuously throughout approximately 270. Of course, a larger diameter first member requires a smaller arc of thread rolling contact, but this arcuate length gives a nice compact machine with `the maximum utilization of the peripheral surface of the first member. This long thread rolling die surface with gradual application of pressure can ybe specified in another manner. Successful results have been obtained when the surfaces are of sufficient length to rotate a work piece in the form of a hollow set screw of approximately one-half inch diameter between l5 and 25 times on its central axis during the thread rolling operation. The -set `screw used was of SAE 1020 steel having a hole hexagonal in cross-section -with the metal Wall about 0.08() inch thick at the corners of the hexagon.

The words generally cylindrical surface, as used herein in this specification and the accompanying claims, includes a surface circular in cross-section (either forming the complete circle or a substantial portion thereof) with either a true cylindrical or a tapered outer surface capable of being roll threaded, includes a true cylindrical surface with tapered threads, and includes other work piece forms having generally cylindrical outer surface.

The fixed and movable dies are readily replaceable to accommodate various blank or work piece sizes. All other operating and auxiliary elements are dimensionally adjustable, as shown and described, to accommodate dimensional changes in the blank.

Various changes in details and arrangement of parts can be made by one skilled in the art without departing from the spirit of this invention or the scope of the appended claims.

What is claimed is:

l. In a machine rfor rolling threads on work pieces with generally cylindrical surfaces, comprising a first member having a rolling surface on which each work piece rolls, a second member including a workpiece carrier means and aceacee a form rolling means, said second member including a slide thereon rotatably carried around said rst member and mounted for relative reciprocation toward and away from said rolling surface on the first member, said form rolling means including a generally cylindrical thread rolling die freely rotatable on said slide for rolling a thread on the generally cylindrical surface of a work piece with said work piece located between said die and said rolling surface of said first member, means operatively connecting said first and Isecond members for relative movement so that said workpiece carrier means and said workpiece carried thereby, form rolling means, and the remainder of said second member move together in the same direction relative to said first member, and a cam operatively connected to said first member, a coacting cam follower on said slide, said cam formed to urge said die and said rolling surface on said first member closer together during relative movement for gradually rolling the thread form deeper on the generally cylindrical surface of the work piece.

2. In a machine for rolling threads on work pieces with generally cylindrical surfaces, comprising a first member having a surface on `which each work piece rolls, a second member with a slide thereon, said slide being mounted for relative reciprocation generally toward `and away from said surface on the first member, ya generally cylindrical thread rolling die freely rotatable on said slide for rolling a thread on the generally cylindrical surface of a Work piece with said work piece located between said die and said surface of said first member, said first and second members connected for relative movement, and a cam fixed yagainst movement relative to said first member, a coacting cam follower on said slide, said cam formed to urge said spaced die and said surface on said first member closer together during relative movement for gradually rolling the thread form deeper on the generally cylindrical surface of the work piece.

3. In a machine for rolling threads on work pieces with generally cylindrical surfaces, comprising a stationary first member having -a peripheral generally cylindrical surface on which each work piece rolls, a second member including a workpiece carrier means and a form rolling means, said second member including a slide thereon mounted for generally radial reciprocation relative to said surface on the first member, said form rolling means including a generally cylindrical thread rolling die freely rotatable on said slide relative to said first member for rolling a thread on the generally cylindrical surface of `a Work piece with said work piece located between said die `and said generally cylindrical surface of said first member, said second member connected to said first member for rotation about the central axis of said first member so that said workpiece carrier means and said workpiece carried thereby, form rolling means, and the remainder of said second member move together in the same direction relative to said first member by rotation together about said central axis, and a cam xed against movement relative to said first member, a coacting cam follower on said slide, said cam formed to urge said die and said generally cylindrical surface on said first member closer together during relative rotation together of said slide, workpiece and die about said `axis relative to said first member and cam for gradually rolling the thread form deeper on the generally cylindrical surface of the work piece.

4. In a machine for rolling threads on work pieces with generally cylindrical peripheral surfaces, comprising a first member having a thread rolling die form on its peripheral generally cylindrical surface on which each work piece rolls, a second member with a slide thereon mounted for generally radial reciprocation relative to said surface on the first member, spaced generally cylindrical thread rolling dies freely rotatable on said slide for rolling a thread on the generally cylindrical peripheral surface of a work piece with said work piece located between said spaced dies and said thread rolling generally cylindrical surface of said first member, said first and second members connected for relative rotation, and a cam fixed against movement relative to said first member, a coacting cam follower on said slide, said cam formed to urge said spaced dies and said thread rolling generally cylindrical surface on said first member closer together during relative .rotation for gradually rolling the thread form deeper on the generally cylindrical peripheral surface of the work piece.

5. In a machine for rolling threads on work pieces with generally cylindrical surfaces, comprising a stationary member having a peripheral generally cylindrical surface on which each work piece rolls, a carrier rotatably mounted on said member for rotation about the central axis of the cylindrical surface on said member, means for rotatably driving said carrier about said axis, a slide slidably mounted on said carrier `for generally radial reciprocation relative to said surface on the member and relative to said carrier, a generally cylindrical thread rolling `die freely rotatable on said slide for rolling a thread on the generally cylindrical surface of va work piece, said die and surface being constructed so that said work piece is located between said die and said generally cylindrical surface of said member and is carried with said slide and carrier about said axis, said die and said cylindrical surface forming a work piece carrier rnaintaining the axis of said work piece generally fixed relative to said slide during said rotation, a stationary cam fixed against movement relative to said `first member, and a coacting cam follower on said slide, said cam extending in an arc around said axis and located to urge said die by said follower toward said generally cylindrical surface on said member during rotation of said carrier about said axis for gradually rolling the thread form deeper on the generally cylindrical surface of the work piece.

6. In a machine for rolling forms on workpieces with generally cylindrical surfaces, comprising two stationary members with the first having a peripheral generally arcuate surface and the second having a more generally arcuate surface, one of said generally arcuate surfaces being located generally equidistant from a central axis and being a form rolling surface on which each workpiece rolls, a carrier rotatably mounted on said members for rotation vabout the central axis of the arcuate form rolling surface, means for rotatably driving said carrier about said axis, a slide slidably mounted on said carrier for generally radial reciprocation relative to` said one arcuate surface and relative to said carrier, two generally cylindrical forin rolling dies arcuately spaced apart about said axis and freely rotatably secured to said slide for rotation about die axes generally parallel to said central axis for rolling a form on the generally cylindrical surface of a workpiece held between said two dies and said one form rolling surface, said dies and said one surface being constructed so that said workpiece is located between said dies and said generally arcuate form rolling surface and is carried with said slide and carrier about said central axis, said dies and said generally arcuate form rolling surface forming a workpiece carrier maintaining the axis of said workpiece generally fixed relative to said slide `during said rotation and generally parallel to said central axis, the other of said arcuate surfaces forming a stationary cam fixed against movement relative to said one arcuate surface, and a coacting cam follower on said slide, said cam extending in an arc `around said central axis and located to urge said dies by said follower toward said one generally arcuate form rolling surface during rotation of said carrier about said central axis for gradually rolling the form deeper on the generally cylindrical surface of the workpiece.

9 UNITED STATES PATENTS 1891 n 1899' D 1917 19.7.9y

10 Draper Ian. 31, 1939 Shera May 20, 1941 Parker et a1. Apr. 10, 1951 Prutton May 21, 1957 FOREIGN PATENTS Great Britain Mar. 3, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,048,065 August 7, 1962 Daniel Ho Prutton It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l, line l5, for "October 21, 19593" read October 21, 1953 column 3, line 5, for "msut" read must line 55, for "threaded" read thread column 5, line 42, strike out "or withdrawn from between"D Signed and sealed this 11th day of December 1962.

SEAL) kttest:

ERNEST w. swIDER DAVID L. LADD testing Officer Commissioner of Patents 

